1. Field of the Invention
The present invention relates to a motorcycle, and particularly relates to a motorcycle having an improved intake air passage structure.
2. Description of the Background Art
For the purpose of increasing the efficiency of air intake in a motorcycle engine, Japanese Patent Laid-open Publication No. 2004-115018 has proposed providing an air passage through a portion of a vehicle body frame. In this published reference, a duct member, which directs fresh air to the air passage, is oriented longitudinally in a front-rear direction of a vehicle body. The air is first introduced through a fresh air inlet, located frontward of the vehicle body frame, and is then routed to the duct member.
In the known motorcycle having such a structure, the air intake efficiency is increased. However, in addition to increased air intake efficiency, further benefit would be achieved if changes in negative pressure (vacuum) within the air routing duct member, due to opening and closing of a throttle, and reducing pipe resonance of the air routing duct member could be further reduced.